SEARCH Articles Figures Tables 2 -Electron-2 -proton transfer 20-electron transition state A perspective A transition states A-Protons A-coupling Coupling of electronic states Coupling of protons Coupling states Electron coupled Electron coupled transfers Electron coupling Electron proton Electron protonation Electron transfer coupling Electron transfer electronic coupling Electron-proton coupling Electronic coupling Proton coupled electron transfer Proton coupling Proton transfer coupled Protonated state Protonation state Transfer of electron Transfer of proton Transfer transition Transition coupling Transition electronic states Transition state proton transfer Transition state protonation Transitions perspective